During the manufacture of flip-chip dies, it is important to detect fine cracks in these dies, including vertical cracks. These cracks can form during the making of the die itself, or during the removal process when separating the die from a ceramic substrate. Standard acoustic microscopy has been used in the past in an attempt to detect these cracks. However, because standard acoustic microscopy uses only planar waves from above the sample which are traveling downward, vertical cracks in a die might be impossible to detect, as they may have little or no cross-sectional area in the z-axis.
Another problem that exists is the construction of the transducer. Because the transducer must be capable of both transmitting and receiving acoustic energy signals in a single device, this leads to increased complexity and costs during its manufacture. Also, because the flip-chip dies are often encapsulated with a plastic or other material which have differing acoustic energy velocities, usually at least two different frequencies of acoustic energy are propagated during the testing process. Further, because the size of a flip-chip die is steadily decreasing, and with it a need to detect smaller and smaller cracks, this leads to a requirement for higher level frequencies of acoustic energy for testing. These factors all contribute to increased costs for the manufacture of transducers that possess the necessary capabilities.